The over-all aim of this project is to determine the chemical differences between identified neurons that contribute to their functional differences. Our initial efforts have concentrated on the identification of synaptic transmitter compounds and the mechanisms by which nerve cells regulate their accumulation. Our approach is to bring together physiological and anatomical techniques with microbiochemical studies in a multi-discipline study. A simple nervous system (the lobster nervous system) was selected for these studies because of its favorable anatomy. Neurons are large, relatively few in number (compared to vertebrates) and axons and cell bodies of single physiologically identified nerve cells can be isolated repeatedly from a series of animals. This allows one to carry out a detailed chemical analysis on a single type of functionally identified neuron. Our past studies have been concerned with gamma-aminobutyric acid, the inhibitory transmitter compound at lobster neuromuscular junctions and glutamic acid, the leading candidate for the excitatory transmitter substance. Recent studies have centered around the identification and regulation of accumulation of the lobster sensory transmitter compound. Several preliminary lines of evidence suggest that acetylcholine may function in this role. The possible transmitter role of octopamine the phenolamine analogue of norepinephrine is also being investigated.